I discovered this was possible recently when cleaning the loo !!
You might already do this but if not try it

If you use the type of toilet bowl cleaner which clips over the rim and consists of a liquid filled capsule connected to a plastic grill... when the capsule is empty dont buy a replacement, just pull the two pieces apart and refill with disinfectant or bleach straight from the bottle. It costs a fraction of the price of new rim blocks.

Thanks Taff, You're right. It's not mean to not buy a plasticy toilet cleaner thingy, if you can get one free, that's being frugal. I'll pop onto the other topic of mean - frugal, and put my bit there.